Air filters are used to purge unwanted substances from air. By way of example but not limitation, air filters are commonly used in laboratories to purge unwanted substances from the air in fumehoods before the air is vented from the fumehood, e.g., to the atmosphere (in the case of a ducted fumehood) or to the ambient air of the laboratory (in the case of a ductless fumehood).
In the laboratory application noted above, the air filter typically uses activated carbon granules to purge unwanted substances from the air. Activated carbon granules are generally preferred for use in air filters because the activated carbon granules are very effective in purging solvents from the air. Furthermore, the use of activated carbon granules is generally highly advantageous, since the activated carbon granules are easily handled, and since they naturally pack into an enclosure with spaces therebetween so as to provide high surface area contact with excellent air flow. Typically, the activated carbon granules are disposed in a simple filter frame, captured between two opposing screens (e.g., meshes, grills, etc.) which pass air therethrough but retain the activated carbon granules therebetween.
While activated carbon granules are extremely effective in purging solvents from the air, they are largely ineffective in purging acids from the air. As a result, where acids may be used within a fumehood, special additives (e.g., rare earth metals, organic metal catalysts, etc.) must be added to the activated carbon granules in order to purge acids from the air. However, these additives tend to reduce the effective surface area of the activated carbon granules, thereby reducing filter capacity. Furthermore, these acid-purging additives are generally only modestly effective in purging acids from the air, and in many cases can include relatively toxic materials which may be released in the air by the air flow through the filter.
Thus it will be seen that incorporating acid-purging additives with the activated carbon granules results in an air filter with reduced efficiency for purging solvents and which has only modest effectiveness for purging acids.
Thus there is a need for a new and improved air filter which is highly effective in purging both solvents and acids from the air and which works with high efficiency and without using toxic additives.